In recent years, there has been a significant growth in the number, size and power density of data centers. This has been fueled by paradigms such as software as a service, cloud computing, and a whole gamut of Internet-based businesses, social networking sites and multimedia applications and services.
Due to the increased dependence on Internet services, data center availability is assuming greater significance. For companies that depend heavily on the Internet for their operations, such as on-line financial services, service outages can be very expensive, easily running into millions of dollars per hour. A widely used design principle in fault-tolerance is to introduce redundancy to enhance availability (the percentage of time that a system provides service at or above the expected and/or required level). This allows use of inexpensive commodity components—having low availability individually—to provide high availability as an aggregate.
This principle is widely practiced in the industry by companies that use commodity hardware and redundant architectures with software control to mask failures and increase availability. However, since redundancy leads to additional use of materials and energy, it is expected to have a negative impact on sustainability.
The drawings referred to in this description should not be understood as being drawn to scale unless specifically noted.